This is really good. 'Light gun' shooter games can get boring for me real fast but the fact that you move the player around the train avoids this. I'd like be able to stop reloading half way to take out the next enemies and being able to take cover while reloading would be good.
Great variety in the attackers - sticks of TNT etc.
Some train sounds would greatly enhance the atmosphere.
I didn't make it to the front of the train ...... yet ;).